At the beginning of the next decade, the world’s first final repository for spent nuclear fuel will begin operating close to the Olkiluoto nuclear power plant on the west coast of Finland. The final disposal of spent nuclear fuel from the power companies Teollisuuden Voima and Fortum will take place in massive, copper-cast iron disposal canisters around 400 metres deep in the bedrock at Olkiluoto.
– The intention is to continue operations at the repository for 100 years. After then, all underground openings will be backfilled and the above-ground facilities will be dismantled and landscaped. No supervision measures are required for this passive solution, says Tiina Jalonen, Senior Vice President, Development, at Posiva.
– There is huge international interest in us.
Hazardous materials will remain underground
Final disposal will be based on multiple barriers, ensuring that no spent radioactive fuel contaminates the natural environment or comes within reach of people.
The bedrock will serve as a natural barrier. This will be complemented by man-made, engineered barriers. These will include copper-cast iron disposal canisters in which the fuel elements will be placed; a buffer of bentonite clay surrounding the canisters in the deposition holes, in order to hinder water flow and protect the canisters from damage; filling the tunnels with clay containing backfill material; and plugging the tunnel’s mouth.
– Various models have shown that, even if one or more of the barriers fails, no harmful substances will reach the ground surface, says Johanna Hansen, Project Coordinator.
Construction progressing in phases
The safety of final disposal has been ensured by thorough planning and multi-year research projects in which VTT has participated.
– Testing is now underway in the ONKALO underground research facility. The construction of ONKALO has enabled us to study the bedrock at Olkiluoto and the construction methods
developed. We have recently been testing the final disposal procedures. ONKALO research
facility will be completed during this year, and later it will be a part of the repository, says Jalonen.
Construction of the repository will begin as soon as ONKALO is ready. The ventilation and hoist equipment are already being built. They will serve ONKALO in the initial stage, as well as the repository later on.
Construction work has also begun on the foundations of the encapsulation facility. In the encapsulation facility, the spent nuclear fuel will be dried and placed in canisters, which will be closed, welded, inspected and sent to the final disposal repository or interim storage.
– Passages have already been built to the underground storage facilities. We will begin building the central tunnels during the next phase and the actual final disposal tunnels in a few years’ time. The first underground final disposal areas are now under planning, Hansen says.
R&D programmes providing further details
– In our current R&D programmes, we are exploring additional issues related to the safety of final disposal; the Finnish Radiation and Nuclear Safety Authority STUK required Posiva to resolve such issues when granting it a construction license in November 2015, says Jalonen.
The programmes involve studying the final disposal canisters and spent fuel, the buffers, the backfilling and plugging of the tunnels, the repository site and preparations for production. In addition to fulfilling the requirements set by STUK, the goal is to obtain additional information for the design and construction of the encapsulation and final disposal facility.
– This is important work. Posiva’s employees feel that it is great to be part of this project. We are highly motivated by the idea of solving the global nuclear waste challenge, says Jalonen.
Setting their sights on a permit
Further information is also needed for a so-called safety case, which Posiva must complete in order to apply for a operating license for the final disposal site. Posiva intends to submit the safety case in 2020.
A great deal of planning and testing is required in order to obtain the license. Posiva must also demonstrate that final disposal will work as assumed.
– The planning phase of a full-scale system test is now under way. We will perform a final disposal test in demo facilities and deposition holes at ONKALO, where we will use prototype machines intended for installing the engineered barriers as well as existing, actual barrier components. Of course, we will not yet be using spent fuel in the canisters, says development engineer Pasi Rantamäki.
VTT is acting as the main consultant in the design of the system tests.
VTT involved in technical development work
– VTT has long played a key role in our R&D work. We have been using VTT’s expertise in areas such as canister design, the thermal dimensioning of the repository, cement and clay materials development, and the development, testing and modelling of the bentonite clay buffer. This will enable us to evaluate the long-term behaviour of the final disposal system. VTT is also playing a major role in the development of the inspection techniques for the canisters, says Jalonen.
– Our multi-disciplinary final disposal project is being supported by VTT’s many areas of expertise. In certain sub-areas, VTT experts have often been able to introduce a new and innovative method from a completely different field, says Hansen.
Jalonen points out that the scientific community behind VTT has brought credibility to its work.
– The building and maintenance of trust are very important in our field, she points out.
The Posiva personnel are highly satisfied with VTT’s systematic practices and prompt reports. They also praise VTT for recruiting skilled staff in place of retiring experts.
Jalonen explains that Posiva no longer does its own basic research, but sources it externally when necessary.
Successful research cooperation
The closure of the repository was studied as part of the joint European DOPAS project, which will end in August. Under the POPLU sub-
projects, VTT participated in a full-scale plugging demonstration carried out in ONKALO.
– Edgar Bohner, the manager of VTT’s Infrastructure Health Team, led the instrumentation and monitoring team, which performed the instrumentation for the POPLU test plug and developed the pressure testing and water leakage monitoring equipment. Our collaboration went well, and we achieved excellent results, says Programme Manager Petri Koho of Posiva, who is serving as Project Manager for POPLU.
– Our team is supporting Posiva in identifying the best and safe final disposal solutions. We develop materials and our specialism lies in the development of low pH concrete, Bohner says.
Bohner’s team mates are designing barriers and are investigating the industrial manufacture of buffer blocks from bentonite clay. Among other innovations, they are developing wireless sensors that send monitoring signals from the final disposal repository to the outside world. The team recently received an order for the design of test arrangements for full-scale system testing to be performed in ONKALO.
Posiva and VTT have been collaborating for around twenty years. Antti Poteri, a Principal Scientist at VTT, already performed research for Posiva’s predecessor, the nuclear waste agency of TVO. His special area is modelling.
– My research focuses on the migration of radionuclides through the bedrock. Our modelling calculations were used as a part of the safety case that was prepared in support of the Posiva’s construction license application. Posiva is now getting prepared to submit its application for an operating license of the final repository and the research focus has moved to drawing up a new safety case, Poteri says.
- An expert organisation established in 1995.
- In charge on behalf of its owners of the final disposal of spent nuclear fuel and other expert tasks related to nuclear waste management.
- Owners: Teollisuuden Voima (TVO) 60%, Fortum Power and Heat 40%.
- Personnel: around 80 persons + some 200 subcontractors and consultants.
- Turnover 2015: around EUR 63 million.
- Its service business subsidiary, Posiva Solutions, was founded in 2016.